Cable pulley

ABSTRACT

A cable pulley has a cable groove extending in the form of a serpentine around the periphery of the pulley.

11111166 states P616111 119] 1111 3,844,537 Rinio Oct. 29, 1974 [541 CABLE PULLEY [56] 8616166665 Cited [76] Inventor: Johannes Rinio, UNITED STATES PATENTS be g 7 587,806 8/1897 Fox 74/2305 Odenthal, Germany 2,802,366 8/1957 Borner 254/191 UX [22] Wed: July 9, 1973 3,104,792 9/1963 Walton 266/183 x pp No: 377,651 FOREIGN PATENTS GR APPLICATIONS 1,233,174 5/1971 Great Britam 74/2305 27,210 12 1902 Switzerland 74/2305 [30] Foreign Application Priority Data July 8, 1972 Germany 2233659 P imary Examiner-Allen N. Knowles June 5, 1973 Germany, 2328474 Attorney, g or FirmJ0hn D n m y r July 4, 1973 Germany 2334045 [57] ABSTRACT g 254/191 226/ A cable pulley has a cable groove extending in the [58] Field 61 Search 254/1755, 191; 226/183; f a Serpent amund the perphery the 19 Claims, 27 Drawing Figures CABLE PULLEY The invention relates to a cable pulley having a cable groove arranged on the periphery of the pulley, especially for driving a cable of unlimited length.

The known cable rollers or cable pulleys provided with a circumferential cable groove and utilized as drive pulleys for cables, have the disadvantage of a limited drive capability which depends from the angle of cable contact. In order to increase the drive capability of the cable pulley in drive systems having a single pulley, in which the angle of cable contact cannot be increased, it has already been proposed to utilize wedgeshaped grooves wherein due to the shape of the groove the coefficient of friction can be significantly increased so that greater tension forces can be transmitted from the cable pulley to the cable. However, wedge-shaped grooves have the disadvantage that the cable wears down the wedge surfaces so that the clamping action becomes smaller and therefore the greater friction between the cable pulley and the cable is again decreased.

It is an object of the invention to eliminate these disadvantages and to provide a cable pulley which has, in comparison with the known cable pulleys, a greater drive capability, even if the shape of the groove and the angle of cable contact in the peripheral direction recontact and the same. diameter a greater cable length is engaged on the periphery of the cable pulley in comparison to a cable pulley where the cable groove is provided in a plane of the cable pulley. In this manner it is possible to transmit greater tension forces to the cable.

The cable groove has preferably the form of a sine curve about the periphery of the cable disc. However, it is also possible to provide a cable groove in the form of a polygonal course, wherein .the cable groove may comprise segments extending parallel to the pulley surfaces and segments extending obliquely to the pulley surfaces. The selection of the groove course depends on the type of cable to be utilized. Because the cable is subjected to a back fiexion stress the sine curve is more appropriate for low flexibility steel cables having a twist in opposite directions, whereas for a cable disc with a groove in the formof a polygonal course, for example, hemp or jute cables may be utilized.

- The cable pulley may comprise two pulley parts that are displaceable in the axial direction relative to each other, wherein each pulley part presents on its peripheral edge facing the other pulley part half the cable groove. With this construction of the cable pulley it is possible to change the width of the groove in order to exert additionally a lateral clamping action on the cable in the groove when the groove section is appropriately selected. The clamping action is here not constant along the complete length of the groove, because a displacement of the pulley parts relative to each other has a smaller effect in the segments of the groove extending parallel to the pulley surfaces than in the segments extending obliquely to these surfaces. In the latter segments the clamping action is therefore greater than in the segments extending parallel to the pulley surfaces when the two pulley parts are pressed one against the other.

According to a further feature of the invention the two pulley parts are arranged on a shaft so as to be rotatable relative to each other, whereby an additional clamping of the cable in the cable groove may be obtained. According to the invention the possibility exists also to arrange one of the pulley parts so as to be rotatable and axially movable relative to the other "pulley which is fixedly mounted on the shaft. This construction may be advantageously obtained by guiding the rotatably movable pulley part by meansof a thread on the shaft.

The cable groove may have in a known manner a semicircular section. However, it is preferably square shaped so that on the one side the cable may move in the obliquely extending segments better on the cable pulley and so that on the other side a rectilinear support surface is provided on the pulley for the cable during rotation so that the cable does not have the tendency to slip upwardly out of the groove.

It is particularly appropriate to provide a cable groove with a semi-elliptical section wherein the greater diameter of the ellipse is normal to the axis of the pulley. In such an embodiment the cable can be well supported at the side flanks of the groove and in case of higher tension forces thecable is pulled deeper and deeper into the groove and it is more and more fixedly clamped therein.

in cable pulleys with a serpentine cable groove which rotate only in one direction and which pull the cable always only in one direction the difficulty exists that the cable travelling over the pulley is constantly subjected to a considerable stress which acts always along the same line laterally on the cable, when the cable is not rotated about its axis during its reciprocating movement, but such a rotation is normally not possible and also undesired in order to prevent a cork and kink formation. Furthermore the possibility is not excluded that the cable may move up and slip out of the groove during'a high load. I I

It may therefore be appropriate to provide an undercut profile for the cable groove at least in the region of their segments extending obliquely to the pulley surfaces.

With this type of construction it will be necessary to guide the arriving cable in accordance with the course of the groove so that it may enter without constraint into the cable groove. Such a cable guide may also prove to be appropriate for the other groove forms.

According to a particularly advantageous feature of the invention an excellent entering of the cable into the groove may also be obtained without a special cable guide means when the radial central plane of the cable groove, depending on the direction of the cable groove, oscillates back and forth on the pulley periphery, in such a way that it takes up alternately a position on the one or the other side which is inclined relative to' the plane of the cable pulley. g

This construction has the advantage that the cable running over the cable pulley is clamped in the cable groove at different points of its periphery depending on the direction of the cable groove. Thus the cable wears uniformly at least on half of its periphery. Due to the slippage of the cable the stress of the cable is uniformly distributed along the entire cable length after several reciprocating cable movements.

In accordance with the invention the edges of the undercut cable groove are preferably chamfered. In this way it is obtained that the cable may enter also without special guide means into the undercut cable groove profile and may move out of the cable groove when the cable moves away off the pulley.

The chamfered edges of the undercut cable groove may preferably define an inlet groove located substantially in the central plane of the cable pulley. This construction has the advantage that the cable may move into the cable groove and out of this groove without constraint, while all the advantages of the serpentine shaped cable groove and of the undercut profile are maintained.

For the purpose of an efficient production it is preferable to arrange the undercut cable groove on the periphery of two rim halves which are fixed on the outer periphery of a planar, circular disc and which are connected to one another.

In the embodiment with two pulley parts rotatable relative to each other the pulley parts may be connected to each other by at least one connecting element of elastic material.

This construction has the advantage that the two pulley parts may still be rotated relative to each other under the influence of the loaded cable but that at the same time a return force is generated which counteracts unduly high forces acting in the peripheral direction.

The elastic connection element develops its elasticity not only during torsion in the peripheral direction but also in the axial direction because the cable clamped in the cable groove has the tendency to separate the pulley parts. The elastic connection element may follow such an axial separation also to a limited extend and in this way may reduce unduly high clamping forces.

In view of the return force of the elastic connection element the pulley parts which are rotatable with respect to each other are returned to their initial position when the cable is not loaded or removed, and in this position the lateral flanks of the cable groove arranged on the two pulley parts are parallel to each other. It is therefore particularly simple to place a cable over the empty cable pulley or to push the cable in the peripheral direction over the cable pulley, because the cable groove may be slightly larger in the non-loaded condition of the cable than the cable diameter.

According to the invention one cable part may be fixedly mounted on the shaft and the other cable part may be rotatable on the shaft, and the two pulley parts may be locked against axial displacement on the shaft. In this embodiment the elastic connection elements deploy their return force only in the peripheral direction, while the clamping forces exerted in the axial direction on the pulley parts are absorbed and transmitted by means of a shoulder or the like to the shaft. Such a construction is preferable in case relatively soft elastic materials are utilized for the connection element.

According to a particular construction of this embodiment the rim of the one pulley part is U-shaped and half the cable groove is provided on an arm of the U-shaped rim, while the other single or multi-part pulley part is annular and is rotatably mounted on the inner surface of the U-shaped rim, and the single or multi-part elastic connection element is arranged on the inner surface of the U-shaped rim.

In accordance with the invention the connecting element may consist of a ring of rubber or elastic plastic material and may be vulcanized or bonded to the inner surfaces of the pulley parts. This construction is particularly simple and requires no additional measures with respect to the disc parts. However, the disc parts may also be connected together by a plurality of pins of rubber or elastic plastic material which are lodged in apertures or recesses of the disc parts. The number of pins, their thickness and the elasticity of the material determine the return force which acts on the disc parts. The connecting element may also consist of a spiral spring or a leaf spring.

The invention will now be described in greater detail by referring to several embodiments illustrated in the accompanying drawings, in which:

FIG. 1 is a diagrammatic side view of a cable drive having a drive pulley and pressing rollers,

FIG. 2 is a front elevation view of a cable pulley according to the invention,

FIG. 3 is a side view of the cable pulley according to FIG. 1,

FIGS. 4, 4a and 5 illustrate two further embodiments of the invention in front elevation view respectively in side view,

FIGS. 6 to 10 are developments of a peripheral part of cable pulleys having cable grooves of different form,

FIGS. 11 to 14 illustrate partial diametrical sections of the cable pulley according to FIG. 3 along line XX having different groove sections,

FIG. 15 is a partial section of the cable pulley according to FIG. 9,

FIG. 16 is a diametrical partial section of a cable pulley according to the invention,

FIG. 17 is a diagrammatic top view of a partial development of the cable pulley periphery,

FIGS. 18, 19, and 20 are diagrammatic partial sections along lines lIIIlI, IVIV, and VV of FIG. 17,

FIG. 21 is a diametrical section view of a further embodiment of the cable pulley according to the invention,

FIG. 22 is a partial top view of the embodiment of FIG. 21,

FIG. 23 is a partial diametrical section of a modified embodiment of the cable pulley according to FIG. 21,

FIG. 24 is a side view of the embodiment of FIG. 23,

FIG. 25 is a diametrical partial section of a further modified embodiment of the cable pulley according to FIG. 1, and

FIG. 26 is a schematic representation of the elastic connecting element consisting of a leaf spring.

With reference to the drawings, FIG. 1 illustrates the drive for a cable of unlimited length in a diagrammatic representation, such a drive being used, for example, to drive a lift for carrying persons or loads. In this Figure the incoming end of the cable 11 guided around the cable pulley 10 which serves as drive pulley is designated with 11a and the outgoing end of the cable is designated with 11b. The incoming end 11a of the cable is guided over a support and pressing roller 12 and the outgoing end 11b is guided over a pressing roller 13 which are disposed with respect to the drive pulley such that an angle of contact a of about 270 is obtained. The drive pulley 10 is driven by a drive motor (not shown) in the direction of the arrow A whereby the incoming end 11a of the cable is pulled upwardly, while the outgoing end 11b moves off downwardly. For example, the cabin of an elevator may be suspended on the end Ila while on the lower extremity of the outgoing end 11b a counterweight may be fixed. It is also possible to eliminate one of the two rollers I2 and 13.

The cable pulley I0 utilized inthe cable drive of FIG. 1 has a cable groove 14 with a semi-circular section, which groove, as can be seen in FIG. 2, extends in the form of a serpentine around the periphery of the cable pulley l0, i.e., the cable groove is not always lo-' cated in the same plane of the cable pulley but it travels along the periphery of the cable pulley back and forth from one side of the pulley to the other.

In FIGS. 6 to 10 developments of a part of the periphery of different embodiments of cable pulleys 10 according to the invention are represented. In the embodiment of FIG. 6 the cable groove 14 on the peripheral surface 15 has the form of a flat sine curve. In the embodiment of FIG. 7 the cable groove has the form of a polygonal course, having sections 4b extending obliquely to the pulley surfaces 16 and 17, these sections being rounded at their apexes 140.

FIG. 8 shows also a cable pulley in the form of a p0 lygonal course having sections 14a parallel to the pulley surfaces 16 and 17 and sections 14b extending obliquely to the pulley surfaces 16 and 17, wherein the cable groove is rounded at the connection points of the sections 140 and 14b.

FIG. 9 shows a cable groove 14 similar to the embodiment of FIG. 8 but which is not rounded off at the connection points of the segments 14a and 14b.

In FIG. 10 the development of a part of the periphery of a cable pulley is represented, which consists of two pulleypartsIO and 10b. In this embodiment, represented ingreater detail in FIG. 4, one pulley part 10b is fixedly mounted on the drive shaft 18, while the other pulley part 10a is freely journaled on the shaft 18 and is displaceable axially against the pulley part 10b in the direction of the arrows 19. The pulley part 10a is coupled to the pulley part 10b by driving pins 21 extending into recesses formed in the pulley part 10b.

Each of the two pulley parts that are axially movable relative to'each other. is provided with half the cable groove 14 which in this embodiment has a semicircular section and extends in the form of a sine curve over the periphery 15 of the pulley. The groove halves are each provided on the oppositely disposed edge 22 or 23 of the pulley parts. It is apparent that due to an axial displacement of both pulley parts relative to each other thediameter of the cable groove 14 can be var- It may be appropriate to provide an adjustable stop on the shaft for the axially movable pulley part 10a in order to limit its movement in the axial direction. This permits the utilization of different diameter cables and provides furthermore the possibility to compensate for wear of the cable by changing the spacing of the two pulley parts.

It is also possible to arrange the two pulley parts 10a and 10b on the shaft so as to be rotatable relative to each other and possibly also axially movable to each other. If the two pulley parts are rotatable relative to each other, one may obtain an automatic clamping of the cable in the cable groove, so that for the same angles of contact 0: greater forces may be transmitted I over the cable pulley to the cable. In FIG. 4a an embodiment is represented wherein the pulley part 10a is fixedly mounted on the shaft 18, while the pulley part 10b is rotatable with respect to the shaft 18 and thus also with respect to the pulley part 10a, and at the same time is also axially movable with respect to the shaft. The pulley part 10b is threaded with an inner thread on a thread 18a of the shaft 18 and may therefore rotate with respect to the fixed pulley part 10a and may axially move with respect thereto. It is apparent that in case of a rotation of the pulley part 10b with respect to the pulley part 10a the section of the cable groove 14- is locally restricted so that a more or less important clamping of the cable located in the cable groove is obtained at these local regions. The clamping of the cable is obtained automatically by the influence of the cable tension force and the friction contact between the cable and the cable pulley. Since with the rotary movement also an axial movement of the disc half 1% occurs the cablepulley, respectively, the cable groove'14 in the cable pulley is automatically adjusted to different cable diameters, wherein at the same time the cable wear is compensated. Due to the axial movement of the pulley part 10b the introduction of the cable into the cable groove is also simplified. In FIG. 4a the broken lines indicate the adjustable pulley part 10b in a position 10b which has a slightly greater spacing from the fixed pulley part 10y than in the position 10b.

It is also possible to eliminate the thread 18a and to mount the pulley'part 10b simply rotatably on the shaft 18. Also in this case one obtains automatically a clamping of the cable in the cable groove 14. The rotatable pulley part 1012 is placed in rotation by meansof the driven pulley part 10a due to the friction forces.

In FIGS. 11 to 14' different section forms of the cable groove 14 are shown. In the embodiment of FIG. 11 the cable groove 14 is semi-circular and in the embodiment shown in FIG. 12 the cable groove 14 is semi-elliptical wherein the greater diameter 24 of the ellipse is normal to the axis 25 of the pulley. In the embodiment of FIG. 13 the cable groove 14 has a trapezoidal section and in the embodiment of FIG. 14 the cable groove 14 is square shaped.

In the embodiment of FIG. 15 representing a partial section of the cable groove shown in development in FIG. 9, the cable groove 14 has an undercut profile, i.e., thecable 11 is located behind a projection 26 extending partially over the upper side of the cable.

7 The cable pulley 10 of FIG. 16 consists of a flat, circular disc 30 which'is fixedly mounted on a shaft 18 and which supports on its periphery two rim halves 31a and 31b which are welded on their entire surface to the disc 30 or are locally fixed thereto by rivets or bolts 32. The rim halves 31a and 31b of the cable pulley 10 have on their periphery 15 a cable groove 14 which, as

. shown in FIG. 17, extends in the form of a serpentine in the peripheral direction.

As shown in FIG. 16 the cable groove 14 has an undercut profile, i.e., its radial central plane 33 does not coincide with the plane 35 of the cable pulley, but forms with this plane an acute angle B. However, this angle B is not constant along the periphery 15 of the cable pulley 10 but the radial central plane 33 of the cable groove 14 oscillates from one side to the other, depending on the direction of the cable groove 14 moving from one side to the other on the pulley periphery 15, such that the plane 33 assumes alternately a position inclined toward the one or the other side 16 or 17 of the cable pulley plane 34. It is apparent from FIGS. 18 to 20 that the central plane 33 of the cable groove 14 is inclined toward the left with respect to the cable pulley plane 34 when the cable groove 14 is located on the left rim part 31a (FIG. 18) and that the radial central plane 33 is inclined toward the right with respect to the cable pulley plane 34 when the cable groove 14 is in the right rim half 31b (FIG. 20). At a point which is located exactly between these two apexes, the radial central plane 33 is coincident with the cable pulley plane 34 (FIG. 19). It is apparent, that due to this oscillation of the cable groove the contact lines 35 between the cable 11 and the cable groove 14 move continuously to-and-fro on the periphery of the cable so that the cable 11 is always clamped at different points of its periphery.

As shown in FIG. 16, the undercut edges 26 of the cable groove 14 indicated by broken lines are chamfered so that the chamfered surfaces 36 define an inlet groove 37 located substantially in the central plane 34 of the cable pulley. In this case the chamfered surfaces may extend parallel to the flanks 38 of the cable groove or may also have a greater inclination with respect to the central plane 34 of the cable pulley.

FIG. 21 shows a cable pulley 10 which is mounted on a shaft 18. The cable pulley 10 comprises two pulley halves 10a and 10b. The pulley half 10a is fixedly positioned by means of a key 42 on the shaft 18. However, the pulley part 10b may rotate on the shaft 18.

As may be seen in FIG. 22, both pulley halves 10a and 10b are provided on their periphery with a serpentine shaped cable groove 14, whose one flank 14' is formed in the pulley half 10a and whose other flank I4" is formed in the pulley half 10b. In the central region the two pulley halves 10a and 10b have each a recess 44 in which a ring 45 of rubber or elastic plastic material is arranged which is vulcanized or bonded to the inner surfaces of the pulley halves 10a and 10b.

When the pulley half 10a rotates with the shaft 18 the rotatably mounted pulley part 10b lags slightly with respect to the pulley part 10a. In this way the cable is clamped in the narrowing diagonal sections 14b of the cable groove. The clamping pressure is transmitted by the ring 45 from the free pulley part to the fixed pulley part. For the transmission of the clamping pressure a shoulder 47 may be provided on the shaft 18 for each pulley part 10a and 10b. The shoulder 47 prevents an axial displacement of the pulley half and takes up the clamping pressure of the cable acting in the axial directron.

If no cable is located in the cable groove 14 or if the cable is not loaded, the ring 45 of rubber elastic material returns the pulley halves 10a and 10b to the initial position shown in FIG. 22, in which the flanks l4 and 14" of the cable groove on the two cable halves 10a and 10b are parallel to each other.

In the embodiment shown in FIGS. 23 and 24 the pulley halves 10a and 10b have a plurality of apertures 48 distributed over the pulley surfaces and extending completely through the pulley halves 10a and 10b, and in which pins 49 of rubber or elastic plastic material are inserted. Also in this embodiment the rotary motion of the two pulley halves 10a and 10b relative to each other is limited by the elasticity of the elastic pins 49 which return the pulley halves to the initial position when the cable is not loaded.

It is also possible (FIG. 25) that the cable pulley consists of a pulley part 10a whose rim is U-shaped, and of an annular pulley part 10b mounted on the inner surface of the U-shaped rim, wherein one arm 10c of the U-shaped rim and the annular pulley part 10b are provided each with half the cable groove 14, and wherein the elastic connection element 52 is disposed on the inner surface of the U-shaped rim. In order to permit the assembly of the annular pulley part and the elastic connection element with the U-shaped rim the first mentioned elements 10b, 52 may be made in two parts or the straight arm of the U-shaped rim may be removable.

The connecting element may also consist of one or more spiral springs or a leaf spring. FIG. 26 corresponds to the latter embodiment, wherein the line A,, 3,, A B represents a leaf spring 53 connected simultaneously to the non-loaded pulley parts 10a, 10b while the line A,, B A B represents the same spring after a relative rotation B 8,, has occurred between the pulley parts.

It is also possible that in the embodiment of FIGS. 23 and 24 the pins do not extend completely through the pulley halves but are inserted only in pocket holes formed in the inner surfaces of the pulley halves. Also the rubber ring shown in FIGS. 21 and 22 may be partially inserted into the pulley halves and may be connected additionally by tholes to the pulley halves.

The invention is not limited to the embodiments described herein, more particularly there are many different fields of application where a cable pulley according to the invention may be utilized. For example it may be used advantageously in a cable hauling device for pulling and releasing cable of unlimited length. The cable pulley according to the invention may also serve as drive pulley for the drive cables of aerial cable ways or the like.

It is evident that the drive pulley according to the invention must not consist of a full disc but instead may consist of a pulley with spokes. In addition it is possible to select other groove sections if this permits to obtain particular advantages.

What is claimed is:

1. A cable pulley for driving a cable of indefinite length, said pulley having a cable groove, in its outer periphery, extending therearound in a generally serpentine path, said pulley comprising two parts each of which has a portion of said groove therein, said parts being relatively rotatable, about their central axis and movable axially relative to each other.

2. A cable pulley according to claim 1, wherein one pulley part is fixedly connected to a drive shaft, while the other pulley part is rotatable with respect to the first pulley part about said shaft.

3. A cable pulley according to claim 2 wherein the rotatable pulley part is threaded on the shaft.

4. A cable pulley according to claim 1, wherein the cable groove is of semi-elliptical section, and the greater diameter of the ellipse extends normal to the pulley axis.

5. A cable pulley according to claim 1, wherein the cable groove is of trapezoidal section.

6. A cable pulley according to claim 1, wherein the cable groove is of square section.

7. A cable pulley according to claim 1, wherein the cable groove has an undercut profile in the region of portions thereof extending obliquely to the pulley side surfaces.

8. A cable pulley according to claim 1, wherein the radial central plane of the cable groove varies alternately from a position inclined to the one side then to the other side with respect to the cable pulley plane, as a function of the direction of the cable groove, and thereby defining undercut edges.

9. A cable pulley according to claim 8, wherein the respective undercut edges are chamfered.

10. A cable pulley according to claim 9, wherein the chamfered undercut edges define a restricted inlet disposed substantially in the central plane of the cable pulley.

11. A cable pulley according to claim 10, wherein the undercut edges of the cable groove are arranged on the periphery of the two pulley parts. 4

12. A cable pulley according to claim 1, wherein the pulley parts are connected together by at least one connection element of elastic material.

13. A cable pulley according to claim 12, wherein one pulley part is fixedly mounted on a shaft and the other pulley part is rotatable with respect to the shaft, the pulley parts being retained against axial movement on the shaft.

14. A cable pulley according to claim 12, wherein the rim of the one pulley part is U-shaped and is provided with half the cable groove on one arm of the U-shaped form, the other part being annular and rotatably mounted on the inner surface of the U-shaped rim, the elastic connection element being disposed on the inner surface of the U-shaped rim.

15. A cable pulley according to claim 14, wherein the connection element consists of a ring of rubber or the like material and is bonded to the inner surfaces of the pulley parts.

16. A cable pulley according to claim 14, wherein the pulley parts are connected together by a plurality of pins of rubber or the like material said pins being received in apertures in the pulley parts.

17. A cable pulley according to claim 14, wherein the connection element consists of at least one spring.

18. A cable pulley as defined in claim 1 wherein said cable groove is in the form of a sine curve.

19. A cable pulley as defined in claim 1 wherein said cable groove defines a polygonal course. 

1. A cable pulley for driving a cable of indefinite length, said pulley having a cable groove, in its outer periphery, extending therearound in a generally serpentine path, said pulley comprising two parts each of which has a portion of said groove therein, said parts being relatively rotatable, about their central axis and movable axially relative to each other.
 2. A cable pulley according to claim 1, wherein one pulley part is fixedly connected to a drive shaft, while the other pulley part is rotatable with respect to the first pulley part about said shaft.
 3. A cable pulley according to claim 2 wherein the rotatable pulley part is threaded on the shaft.
 4. A cable pulley according to claim 1, wherein the cable groove is of semi-elliptical section, and the greater diameter of the ellipse extends normal to the pulley axis.
 5. A cable pulley according to claim 1, wherein the cable groove is of trapezoidal section.
 6. A cable pulley according to claim 1, wherein the cable groove is of square section.
 7. A cable pulley according to claim 1, wherein the cable groove has an undercut profile in the region of portions thereof extending obliquely to the pulley side surfaces.
 8. A cable pulley according to claim 1, wherein the radial central plane of the cable groove varies alternately from a position inclined to the one side then to the other side with respect to the cable pulley plane, as a function of the direction of the cable groove, and thereby defining undercut edges.
 9. A cable pulley according to claim 8, wherein the respective undercut edges are chamfered.
 10. A cable pulley according to claim 9, wherein the chamfered undercut edges define a restricted inlet disposed substantially in the central plane of the cable pulley.
 11. A cable pulley according to claim 10, wherein the undercut edges of the cable groove are arranged on the periphery of the two pulley parts.
 12. A cable pulley according to claim 1, wherein the pulley parts are connected together by at least one connection element of elastic material.
 13. A cable pulley according to claim 12, wherein one pulley part is fixedly mounted on a shaft and the other pulley part is rotatable with respect to the shaft, the pulley parts being retained against axial movement on the shaft.
 14. A cable pulley according to claim 12, wherein the rim of the one pulley part is U-shaped and is provided with half the cable groove on one arm of the U-shaped form, the other part being annular and rotatably mounted on the inner surface of the U-shaped rim, the elastic connection element being disposed on the inner surface of the U-shaped rim.
 15. A cable pulley according to claim 14, wherein the connection element consists of a ring of rubber or the like material and is bonded to the inner surfaces of the pulley parts.
 16. A cable pulley according to claim 14, wherein the pulley parts are connected together by a plurality of pins of rubber or the like material said pins being received in apertures in the pulley parts.
 17. A cable pulley according to claim 14, wherein the connection element consists of at least one spring.
 18. A cable pulley as defined in claim 1 wherein said cable groove is in the form of a sine curve.
 19. A cable pulley as defined in claim 1 wherein said cable groove defines a polygonal course. 